Mercury interrupter



Dec. 24, 1940 w. s. BRIAN MERCURY INTERRUPTER Filed March 17, 1939 "W 5%H 7 i E 1 0 0 b r 0 C Patented Dec. 24, 1940 UNITED STATES PATENT OFFICEMERCURY INT'ERRUPTER Application March 17, 1939, Serial No. 262,396

2 Claims.

This invention relates to circuit controlling means and morespecifically to automatic circuit interrupters. It has subject-matter incommon with the same type of interrupter as disclosed in my copendingapplications Serial No. 241,383 filed November 19, 1938, and Serial No.241,384 filed November 19, 1938, and deals specifically withimprovements thereover.

With the type earlier disclosed it has been difllcult to obtainoperating frequencies slow enough for various types of apparatus, forexample, fuel pumps. It has also been found that the carbon tip wearsaway to some extent. It is the object of the present disclosure toprovide an interrupter which operates at acomparatively low frequencyand also one in which the life of the carbon tip is substantiallylengthened.

The embodiments of my invention will therefore be better understood byreference to the following specification and claims and illustrations inthe accompanying drawing, in which:

Figure 1 is a vertical section through an interrupter of my invention;

Figure 2 is a similar view of a portion of the 5 interrupter showing adifferent stage in the op eration thereof; and I Figure 3 is a verticalsection through a portion of a modified form of interrupter similar toFigure 2.

0 The present type of interrupter is shown as comprising a main outerenvelope 2 which in the present instance is shown as glass but mayconsist of any type of suitable housing, at least a portion of which isof electrically insulating material so that the two electrodes areelectrically isolated.

The general form of the envelope 2 is tubular and one end of the memberis heated and pressed around an electrode 4 to support the same, saidelectrode 4 projecting into a center chamber 6 a substantial amount. Thelower end of the envelope 2 is also pressed around an electrode assemblycomposed of a metal wire 8 which is staked into a small carbon mass l0and the glass drawn tightly around the two to support the assembly inthe lower end of the envelope.

- The upper end of the carbon mass l0 comprises a small projecting tipI! which projects through a glass partition and extends a short distanceinto the center chamber, the outer envelope being drawn in to form arestricted area ll adjacent this tip. A pool of mercury I6 is enclosedwithin the envelope and the device normally operated in the positionshown, the. mercury flowing down through the restriction l4 and restingupon the 65 end of the electrode I2, a portion of the space surroundingthe electrode I2 being filled only with mercury vapor since the surfacetension of the mercury prevents it from flowing in to all the crevicesas shown in Figure 1.

As current is applied to the two electrodes 4 and 8 and fiows throughthe mercury bath, the mercury actually in contact with the carbon tip [2is heated to such an extent that it is vaporized and this vapor forcesthe body of mercury upwardly to such a position as shown in Figure 2.This of course causes the circuit between the electrodes to be brokenand the weight of mercury causes the mercury to again descend,compressing and condensing the mercury vapor until it again contacts thetip l2 and the cycle is completed. 15 The operation of this device maybe described as autonomic in that it is self-governing and requires noseparate or outside control.

Thus, as in former cases, we have an automatic, periodic circuitinterrupter, but in this instance 20 the restricted neck ll prevents themercury from again coming in contact with the carbon tip I! as soon asit would if the restriction were not present and in this manner slowsdown the normal operation of the device so that it has been 25 possibleto operate tubes of this design at frequencies of from 5 to 30 cyclesper second, for example, and to pass fairly high power currentstherewith. By designing the area of this neck therefore we are able tocontrol to some extent 30 the speed of operation. This geyser efiectalso causes a more rapid quenching of the arc.

Since the carbon tips in these devices have worn and where they wereprovided flush with the glass surface have cratered after long wear to35 such an extent that the mercury does not flow deep enough to causeproper contact, it has been found that in this type of device it issatisfactory to allow the carbon tip to project a certain amount abovethe surface of the glass. As previously explained, the surface tensionof the mercury prevents the same from flowing down around the sides ofthe tip so that actually there is no more carbon surface in contact withthe mercury than if the same had been ground off flush with 5 the glassand therefore I am able to obtain a decided increase in life of thecarbon point and in no way aifect the other characteristics of theinterrupter.

It has also been found that the carbon point so may be coated with avery thin layer of suitable metal for the same purpose; namely, that ofin creasing the life. The metal used must have a high melting point andresist amalgam with mercury. I have found through experimentation thatby coating the end of the carbon button with a layer of molybdenum, suchas at 22, that the surface will last considerably longer and also that Imay control to some extent the characteristics of the interrupter. Bythis is meant that during one complete cycle various interrupters havedifiering off and on times and with this metal coating I have found thatthe on time for the cycle can be increased. In this manner the cycliccharacteristics of the interrupter may be predetermined and definitelydesigned and manufactured. This metal surface may be deposited byelectrodeposition or a small metal clip may be mechanically pressed onthe carbon tip when it is made, either manner operating satisfactorily.

In Figure 3 is shown a modified form of my invention in which instead ofhaving the area directly above the carbon tip l2 tapered, since themercury does not flow around the sides of the carbon, the same may bestraight and merely a cylindrical-necked portion such as 20 may beprovided above the carbon tip it. to give substantially the sameresults.

I claim:

1. In an autonomic interrupter, an envelope, two spaced contacts carriedthereby, a body of mercury adapted to bridge the contacts carried by theenvelope, one of the contacts being oi higher resistance than mercuryand of such area as to cause high current density therein wherebycurrent passing through the juncture of the contact and the mercurycauses vaporization of the latter and displacement and a restriction inthe envelope adjacent the contact to impede the flow of the mercury backto its initial position and thus slow up the cyclic operation of theinterrupter.

2. In an autonomic interrupter, an envelope providing a chamber, a pairof spaced electrodes extending into said chamber, one of said e1ectrodesbeing formed of carbon and projecting a short distance into the chamberand having a definite surface area to provide high current density atgiven operating currents, a restriction in the envelope adjacent thecarbon electrode providing a relatively small chamber, a body of mer-=cury suflicient to bridge the two electrodes whereby when current flowsthrough the mercury and the two electrodes and the heat generated by thecarbon electrode vaporizes some of the mercury in the small chamber, themercury will be forced away from the carbon electrode and out of saidsmall chamber and slowly now back upon condensation of the mercury vaporto again complete the circuit.

WILUAM S. BRIAN.

